1. Field of the Invention
The invention concerns a process and device for manufacturing convex sheets of glass having a substantial bent portion of small radius of curvature.
2. Description of the Prior Art
Convex sheets of glass having a pronounced curvature or bend have been manufactured in the past by placing a flat sheet of glass in a horizontal position on a peripheral convexing frame or "skeleton" and subjecting the glass to a predetermined temperature profile such that when the sheet reaches a bending temperature, the sheet will sink under its own weight to wed or conform to the shape of a support.
Jointed convexing molds have also been utilized to produce convex sheets of glass where the molds comprise elements jointed together which may be bent when a sheet of glass has reached bending temperature.
It is also known in the prior art to additionally heat a sheet of glass in the area of a bend to facilitate convexing of the bend to reduce deformation of areas adjacent to the bend. This has been accomplished by placing in electric resistance element in contact with the area to be bent to provide additional heat to the area while the sheet is heated by a conventional furnace or providing an electro-resistant deposit or coating on a sheet of glass in the area to be bent and then connecting the deposit to a current source.
It is also known that bending of a portion of a sheet of glass may be facilitated by weakening the sheet in the area of the bend by means of a groove in order to obtain a sharp edge. The method has been used to facilitate convexing of a sheet of glass under the effect of its own weight when a sheet is heated.
Bending of sheets of glass to large radii of curvature has been accomplished in the past by utilizing a pressing process in which a sheet of glass is vertically suspended from clamps and the suspended sheet then heated to a bending temperature after which the sheet is engaged by a convex rigid pressing mold and an opposite concave mold comprising several movable elements. This process however is not applicable for producing sheets having a very small radii of curvature.
It is therefore an object of our invention to provide a method and apparatus applicable for the manufacture of convex sheets of glass having substantial bent portions of very small radii of curvature.